Method of improving the printing of polyolefins with water-based inks

ABSTRACT

A method for improving the printing of polyolefins with water-based inks by incorporating into the polyolefin an effective amount of N-ethanol erucamide or N-ethanol oleamide. Optionally a finely divided inorganic material can be added with the N-ethanol erucamide or N-ethanol oleamide.

BACKGROUND

This invention relates to improving the adhesion of water-based inks topolyolefin polymers. In particular this invention is directed toimproving the printing of polyolefin films with water-based inks. Animportant aspect of the present invention is the improved adhesion ofwater-based inks to polyolefin films containing N-ethanol erucamideand/or N-ethanol oleamide.

Olefin homopolymers and copolymers are of commercial importance for themanufacturer of numerous articles such as films and other items. Inorder to be useful for many of these functions it is desirable that thepolyolefinic composition have good slip characteristics. This can bedetermined by measuring the coefficient of friction of the polyolefin.It is of increasing importance that the polyolefinic composition haveexcellent adhesion to water-based inks.

In order to obtain a satisfactorily low coefficient of friction, oftenslip agents are added to the polyolefin to lower its coefficient offriction below about 0.5, preferably below 0.3. Many slip agents andother additives for polyolefins are disclosed in the literature. Theseadditives will lower the coefficient of friction of the polyolefin todesired levels, permitting ready handling of shaped articles and filmsprepared from the polyolefinic material. Polyolefinic polymers havingpoor slip characteristics are difficult to handle when the polymer ismanufactured in the customary manner of large rolls. During storage andsubsequent processing, the low slip films tend to adhere layer to layer.Also such films can encounter large frictional forces in processingequipment that often cause distortions and even tearing of the film,especially when using thin film.

Rowland et al U.S. Pat. No. 2,956,979 discloses inhibiting the blockingtendencies of polyethylene by introducing into the composition a smallamount of an alkylol amide of the structural formula: ##STR1## wherein Ris a saturated aliphatic acyl radical of from about 18 to about 30carbon atoms and R' is an alkyl radical group of 1 to 6 carbon atoms.Toy et al U.S. Pat. No. 3,028,355 discloses the use of diatomaceousearth to reduce the tendency of polyethylene to block. Haeske et al U.S.Pat. No. 3,266,924 discloses the blending of a mixture of finely dividedsiliceous material and a fatty acid amide slip agent into polyethyleneto enhance its slip and blocking properties. Ross et al U.S. Pat. No.3,326,840 discloses the incorporation of a small amount of amono-N-substituted saturated carboxylic acid amide of the formula:##STR2## wherein R is an aliphatic acyl radical having from 12 to 30carbon atoms and R' is an aliphatic group having from 1 to 6 carbonatoms, especially an alkylol group, into a copolymer of ethylene and analiphatic ethylenically unsaturated carboxylic ester to improve itsresistance to blocking and improve its slip properties.

Foster U.S. Pat. No. 3,647,738 discloses blending an amide having theformula: ##STR3## wherein R is an alkenyl radical having 18 to about 22carbon atoms and R' is a divalent hydrocarbon radical containing 3 to 15carbon atoms with an alpha-olefin polymer composition to providecompositions having low blocking and no bloom characteristics and highslip properties.

Wharton U.S. Pat. No. 3,396,137 discloses compositions comprising anethylene polymer and an N-substituted unsaturated carboxylic amidehaving improved properties with respect to the coefficient of frictionand the adhesion of solvent-based printing inks to the surface of thepolymer.

While the foregoing patents and other literature disclose a variety ofadditives that improve the slip and/or blocking properties ofpolyolefins, they are silent on improving the adhesion of water basedinks to said polyolefins. It is necessary that the polyolefiniccompositions containing the slip and blocking agents have excellent inkadhesion, particularly to water based inks and good printability so thatthe molded article, film or other item made from the polymer can besuitably printed. Of late it has become highly desirable forenvironmental reasons, such as to reduce emissions of volatile organiccompounds, that the inks used to print on the polyethylene compositionbe water-based inks.

Accordingly it is an object of the present invention to improve the slipproperties of polyolefinic compositions and simultaneously improve theink adhesion properties, particularly the adhesion of water-based inks.

It is another object of the present invention to improve theprintability of water-based inks on polyolefinic compositions,particularly on films and bags used as packaging material.

Another object of the present invention is to impart the desired slip,printability and adhesion to water-based inks to polyolefin compositionswithout adversely affecting the optical properties of the polyolefin.

Other objects of the present invention will become apparent from theensuing description.

SUMMARY OF THE INVENTION

The method of the present invention comprises incorporating an effectiveamount of specified N-ethanol acid amides into a polyolefin polymerforming a polyolefin composition having improved adhesion of inks,particularly water-based inks.

The ethanol amides particularly useful in the present invention areN-ethanol erucamide and/or N-ethanol oleamide. Optionally, an effectiveamount of a finely divided inorganic material can also be incorporatedinto the polyolefin with the N-ethanol erucamide or N-ethanol oleamide.

DETAILED DESCRIPTION OF THE INVENTION

The present invention provides for polyolefins having improved adhesionto inks, particularly water-based inks. The polyolefins can behomopolymers and copolymers and mixtures thereof.

Among the polyolefins of this description are ethylene and propylenehomopolymers and copolymers. Polyethylene can be low density and highdensity polymeric material. Linear low density polyethylene is ingeneral a copolymer of ethylene and up to about 10 weight percent of asecond olefin, such as propylene, butene, hexene or octene. High densitypolyethylene is normally a homopolymer.

There are, basically, two types of olefin polymerization techniques forpreparing high molecular weight olefin polymers and copolymers. Theoldest commercial technique involves high pressure, high temperature,and the use of a free radical initiator, such as peroxide; these typepolymers are generally known as low density polyethylene (LDPE). TheseLDPE polymers contain branched chains of polymerized monomer unitspendant from the main polymer "backbone" and generally have densities inthe range of about 0.910-0.935 gms/cc.

The other commercially-used technique involves coordination catalysts ofthe "Ziegler" type or "Phillips" type and includes variations of theZiegler type, such as the Natta type. These catalysts may be used atvery high pressures, but are generally used at very low or intermediatepressures. The products made by these coordination catalysts aregenerally known as "linear" polymers because of the substantial absenceof branched chains of polymerized monomer units pendant from the mainpolymer "backbone," and they are also generally known as high densitypolyethylene (HDPE). Linear polyethylene (HDPE) ordinarily has a densityin the range of 0.941 to 0.965 gms/cc.

Also used in the present invention are "linear" type ethylene polymerswherein ethylene has been polymerized along with minor amounts of alpha,beta, ethylenically unsaturated alkenes having from 3 to 12 carbons peralkene molecule, preferably 4 to 8. The amount of the alkene comonomeris generally sufficient to cause the density of the polymer to besubstantially in the same density range as LDPE, due to the alkyl sidechains on the polymer molecule, yet the polymer remains in the "linear"classification; they are conveniently referred to as "linear" lowdensity polyethylene" (LLDPE). These polymers retain much of thestrength, crystallinity, and toughness normally found in HDPEhomopolymers of ethylene, but the highest alkene comonomers impart high"block" characteristics to extrusion-cast films and the high "slip"(i.e. low coefficient of friction) characteristic inherently found inHDPE is diminished.

Other homopolymers which can be used include: polypropylene,polybutene-1, poly(4-methylpentene-1) and the like.

Exemplary of the copolymers of olefinically unsaturated aliphatichydrocarbons which are preferred are ethylene-propylene copolymers,containing about 1 to about 99% by weight, based on the total copolymer,of propylene copolymerized therein, ethylene-butene-1 copolymerscontaining about 1 to about 99%, based on the total copolymer ofbutene-1 copolymerized therein, ethylenehexene-1 copolymers containingabout 1 to about 99% by weight based on the total copolymer of hexene-1copolymerized therein and the like.

The homopolymers and copolymers of olefinically unsaturated aliphatichydrocarbons referred to above can be made by either free radicalcatalyzed high pressure techniques or anionic catalyzed low pressuretechniques known in the art and described in "Crystalline OlefinPolymers" Part I by R. A. V. Raff and K. W. Doak, IntersciencePublishers, NYC 1965 which is incorporated herein by reference.

The ethylene-acrylic acid interpolymers ethylenemethacrylic acidinterpolymers, ethylene-vinyl acetate interpolymers and ethylene-alkylacrylate methacrylate interpolymers of this invention can be made by thefree radical, random interpolymerization of ethylene with thecorresponding comonomer using methods well known in the art includingbulk, solution, aqueous suspension, non-aqueous dispersion and emulsiontechniques in either batch or continuous process.

There are numerous polyolefin resins useful in the present invention.For example, Rexene® high molecular weight, low density polyethyleneresins made by the polymerization of ethylene using a free radicalinitiator at high pressure and high temperature was used in theexperimental work reported in Examples 1-5. These polyethylene resinshave the following properties:

Density 0.921 grams/cc

Melt Index 1.0 grams/10 minutes

Tensile (yield) 1500 psi

Tensile (at break) 2100 psi

Ultimate Elongation 500%

Secant Modulus 50,000 psi

Hardness 48 Shore D

Softening Point (Vicant) 200° F.

Among other polyolefins useful in the present invention areethylene-vinyl acetate copolymer resins such as Rexene® PE 1335 whichhas a density of 0.924 grams/cc; a melt index of 2.0 grams/10 minutesand a vinyl acetate content of 3.3%; linear low density polyethyleneresins such as Dowlex 4047 of Dow Chemical Co. which has a density of0.917 grams/cc and a melt index of 2.3 grams/10 minutes andpolypropylene, such as Petrothene® PP 8000-GK of Quantum Chemical Co.which has a density between about 0.89-0.91 grams/cc and a melt index of5.0 grams/10 minutes. These materials are merely representative ofpolyolefins useful in the present invention which are numerous and canbe selected depending upon the desired properties of the finalcomposition.

Various additives are often incorporated into the polyolefin. One suchgroup of additives are antioxidants such as hindered phenols, phenolicphosphites, secondary arylamines and the like. These antioxidants areused in quantities between about 0.01 to about 1 weight percent of thepolymer. Other additives such as colorants, antiblocking agents,antistatic agents and lubricants are commonly used. Also lubricants areoften incorporated into polyolefin compositions, particularlypolypropylene and high density polyethylene in order to improve theprocessability of the polymer.

As previously indicated, there are many materials known to improve slipand blocking properties of films. In recent years environmental concernshave arisen as to the use of organic solvents. Thus, it has becomedesirable to use water-based inks. The solvent-based inks previouslyused are often considered to be environmentally undesirable. Thematerials previously used as slip and antiblocking agents such asunsubstituted amides of long-chain fatty acids, particularly erucamide,do not provide the polyolefinic polymer with the desired adhesion towater-based inks. This property is provided by the present method.

In general the incorporation of from about 0.05 to about 0.3 weightpercent of the identified N-ethanol acid amides into the polyolefincomposition will provide good adhesion of water-based inks. Largeramounts of the N-ethanol acid amide can be used in many instanceswithout significant changes in the water based ink adhesion propertiesof the composition. In certain instances it is preferred that there isused from about 0.05 to about 0.2 weight percent of the N-ethanol acidamide.

Optionally, the method of the present invention may in addition to theN-ethanol acid amides add other components which further the improvementof the adhesion of the water-based inks to the polyolefin polymer. Forexample, it has been found that the addition of a finely dividedinorganic material can enhance the adhesion to water-based inks of thepolyolefin compositions of the present invention. In general thepresence of from about 0.05 to about 1.0, preferably from about 0.1 toabout 0.5, weight percent of the finely divided inorganic material inthe polyolefin composition will be of value in improving the water basedink adhesion of the polyolefin polymers. Examples of these finelydivided materials are silica, mica, talc, diatomaceous earth and calciumcarbonate.

The method of the present invention can be performed by admixing thepolyolefin polymer and the N-ethanol acid amides by various methods.

One method is to blend a masterbatch of the polyolefin polymercontaining the N-ethanol acid amide and other additives. This can beaccomplished by grinding polyolefin pellets in a mill to form a coarsegranule. The N-ethanol acid amide and other additives are melted ontothe surface of the polyolefin granules with the use of a heat lamp. Thenthe granules are mixed and the mixture is extruded through a capillarydie to form a strand which is pelletized. If desired, the pelletizingprocedure can be repeated as many times as desired so as to insureadequate mixing of the components.

The masterbatch can then be added to virgin polyolefin polymer byshaking and tumbling the masterbatch and polyolefin pellets. Then themixture can be converted into the desired product by extrusion, blowmolding, blow extrusion, compression molding or other commercial method.

When an extrusion is desired, the mixture can be extruded through atwo-stage mixing screw with a 3:1 compression ratio and a 20:1length:diameter ratio, although other equipment can be used. Thetemperature of the barrel and die are controlled. As the molten plastictube emerges from the die it can be blown with air to the predetermineddiameter and cooled with air.

Also the method of the present invention can be performed by casting afilm by extrusion through a slot die using a simple screw extruderhaving characteristics such as those for the aforedescribed two-stagemixing screw. Similar test results are obtained from cast films as withblown films.

This N-ethanol erucamide of the present invention can be prepared byreacting an ethanolamine and a methyl ester of fatty acids, such aserucic acid or oleic acid. This general preparation of an amide isdescribed in the literature.

In order to demonstrate the usefulness of the present invention inimproving the adhesion of water based ink a series of experiments wasperformed.

Samples of polyolefin polymers (10"×5") were corona treated in two pathsfor a total of 50 seconds using a high frequency corona treater equippedwith a 2 5/8 inch field effect electrode (Model BD-20C made byElectro-Technic Products, Inc.). The field electrode is held at about1.5 centimeters from the film surface during the corona treatment.Printability tests are performed on the film one week after the coronatreatment. A stripe (10"×23/4") is made on the film with a water-basedink, Hydropoly Red Ink, S89-4710B from Sun Chemical Co. using aspring-loaded handproofer having 23/4 inch printing width. The printedfilm is dried in an oven at 160° F. for 20 seconds. The appearance ofthe print is rated good (G), fair (F) or poor (P) with respect to thesmoothness of the ink coverage and the presence of visual pinholes.

The adhesion of the ink is evaluated by pulling a piece of Scotch 600tape off the printed surface to determine how much ink remains on theprinted surface. The ink adhesion was determined on a scale from 0 to 10with a zero representing zero ink adhesion and 10 representing 100% inkadhered to the printed surface. Ink adhesion determination were made ontwo different product segments and the average reported in the tables.

The coefficient of friction (COF) was determined by ASTM D1894-75 movingsled/stationary plane test method using an Instron 1130 UniversalTesting Instrument. Slip measurements were made one week after extrusionon five different film segments and the average reported in the table. ACOF greater than 0.5 is considered poor, 0.3 to 0.5 fair and 0.3 orbelow considered good. It is the good adhesion of water-based inks topolyolefins having the desired good slip that is sought by industry andas demonstrated in the following examples has been found by the presentinvention.

EXAMPLE 1

Compositions containing N-ethanol erucamide of the present inventionincorporated into low density polyethylene resin compositions wereextrusion blown to films and their properties compared to low densitypolyethylene films containing either no additive or control additives.The results as reported below demonstrate the improvement in theadhesion of water-based inks to polyolefin films containing N-ethanolerucamide.

    ______________________________________                                        N-ethanol                                                                     erucamide                                                                              Control  Microken 801.sup.3 Ink                                      (ppm)    (ppm)    (ppm)        C.O.F.                                                                              Adhesion                                 ______________________________________                                        2000       0        0          0.25  5.8                                      2000       0      1500         0.14  7.3                                      0          0        0          0.95  10.0                                     0          0      1500         0.73  10.0                                     0        2000.sup.1                                                                               0          0.20  0                                        0        2000.sup.1                                                                             1500         0.14  0                                        0        2000.sup.2                                                                               0          0.64  2.6                                      0        2000.sup.2                                                                             1500         0.38  1.0                                      ______________________________________                                         In all experiments the printability was found to be good.                     .sup.1 erucamide                                                              .sup.2 Nethanol stearamide                                                    .sup.3 Microken 801 is a diatomaceous earth from Witco Co.               

EXAMPLE 2

The procedures of Example 1 were repeated incorporating 2000 ppmN-ethanol erucamide along with 1500 ppm each of CaCO₃, Microken 801,mica, silica or talc into the low density polyethylene resincompositions with the following results:

    ______________________________________                                        Run    Additive       C.O.F.  Ink Adhesion                                    ______________________________________                                        1      Calcium        0.16    4.5                                                    Carbonate                                                              2      Microken 801   0.14    7.3                                             3      Mica           0.24    4.0                                             4      Silica         0.12    4.5                                             5      Talc           0.15    3.5                                             ______________________________________                                    

In each experiment the printability was found to be good.

EXAMPLE 3

The procedures of Example 1 were repeated with low density polyethylenefilms containing either N-ethanol erucamide or erucamide (control) witheach sample being subjected to a different corona treatment time to givethe following results:

    ______________________________________                                               Additive    Corona Treatment                                                                            Ink                                          Run    (ppm)       Time (Second) Adhesion                                     ______________________________________                                        1      2000.sup.1  50            0                                            2      2000.sup.1  100           0.5                                          3      2000.sup.2  50            5.8                                          4      2000.sup.2  75            9.2                                          5      1000.sup.2  50            9.5                                          6      1000.sup.2  100           10.0                                         ______________________________________                                         .sup.1 erucamide                                                              .sup.2 Nethanol erucamide                                                

In each experiment the printability was found to be good.

EXAMPLE 4

Additional experiments in accordance with the procedures of Example 1were performed with the following results.

    ______________________________________                                               N-Ethanol                                                                     Erucamide Microken 801       Ink                                       Run    (ppm)     (ppm)        C.O.F.                                                                              Adhesion                                  ______________________________________                                        1       500        0          0.46  7.9                                       2       500      1500         0.19  8.9                                       3      1000        0          0.24  9.5                                       4      1000      1500         0.15  9.7                                       5      2000        0          0.25  5.8                                       6      2000      1500         0.15  7.3                                       7      2000      10000        0.15  7.7                                       8      3000        0          0.21  2.9                                       9      3000      1500         0.14  4.2                                       ______________________________________                                    

In each experiment the printability was found to be good.

EXAMPLE 5

The procedure of Example 1 were repeated using low density polyethylenepolymer containing N-ethanol oleamide in accordance with the presentinvention and with the following results:

    ______________________________________                                              N-Ethanol                                                                     Oleamide   MicroKen 801        Ink                                      Run   (ppm)      (ppm)        C.O.F. Adhesion                                 ______________________________________                                        1      500         0          0.38   9.8                                      2      500       1500         0.22   9.6                                      3     1000         0          0.25   8.1                                      4     1000       1500         0.20   9.4                                      5     2000         0          0.23   6.0                                      6     2000       1500         0.12   5.6                                      ______________________________________                                    

In each experiment the printability was fair to good.

EXAMPLE 6

Example 1 was repeated using linear low density polyethylene (LLDPE),polypropylene (PP) and ethylenevinyl acetate copolymer (EVA) with thefollowing results:

    ______________________________________                                                      N-ethanol                                                                     Erucamide MicroKen 801    Ink                                   Run  Polymer  (ppm)     (ppm)     C.O.F.                                                                              Adhesion                              ______________________________________                                        1    LLDPE      0         0       >1.0  9.0                                   2    LLDPE     500      3000      0.37  9.1                                   3    LLDPE    1000      3000      0.26  5.0                                   4    PP         0         0       0.77  7.3                                   5    PP       2000      3000      0.30  5.1                                   6    EVA        0         0       >1.0  9.7                                   7    EVA      1000      3000      0.23  4.3                                   ______________________________________                                    

In each experiment, the printability was good.

EXAMPLE 7

The procedure of Example 1 were repeated using low density polyethyleneresin and a mixture of N-ethanol acid amides which has a weight percentcomposition similar to that of rapeseed oil, as follows:

    ______________________________________                                        N-ethanol erucamide   46.9 wt. %                                              N-ethanol eicosenamide                                                                              7.4 wt. %                                               N-ethanol linolenamide                                                                              8.7 wt. %                                               N-ethanol linoleamide 14.0 wt. %                                              N-ethanol oleamide    14.6 wt. %                                              N-ethanol stearamide  1.1 wt. %                                               N-ethanol palmitamide 3.3 wt. %                                               ______________________________________                                    

The results of this test were as follows:

    ______________________________________                                                      N-ethanol                                                                     Acidamide MicroKen 801    Ink                                   Run  Polymer  (ppm)     (ppm)     C.O.F.                                                                              Adhesion                              ______________________________________                                        1    LDPE     1000      0         0.29  9.5                                   2    LDPE     1000      1500      0.24  9.9                                   3    LDPE      500      0         0.38  9.9                                   4    LDPE      500      1500      0.24  9.7                                   5    LLDPE      0       0         >1.0  9.0                                   6    LLDPE    1000      3000      0.23  5.3                                   7    PP         0       0         0.62  7.9                                   8    PP       2000      0         0.32  5.2                                   ______________________________________                                    

In each experiment, the printability was good except in Run 6 whereinthe printability was fair.

EXAMPLE 8

The procedures of Example 1 were repeated using a 50/50 blend ofN-erucyl lactamide and N-ethanol erucamide in low density polyethylenewith the following results:

    ______________________________________                                             N-ethanol N-ethanol                                                           lactamide erucamide  MicroKen      Ink                                   Run  (ppm)     (ppm)      801 (ppm)                                                                             C.O.F.                                                                              Adhesion                              ______________________________________                                        1     500       500       1500    0.27  9.3                                   2    1000      1000       1500    0.24  6.2                                   ______________________________________                                    

In each experiment, the printability was good.

EXAMPLE 9

In order to demonstrate the selective advantage of the N-ethanol acidamide of the present invention, the procedures of Example 1 wererepeated using other N-alkylol acid amides outside of the scope of thepresent invention with the following results:

    __________________________________________________________________________       N-(3-hydroxy                                                                           N-(4-hydroxy      Microken                                           propyl)-erucamide                                                                      butyl)-erucamide                                                                       N-(5-hydroxy                                                                           801      Ink                                    Run                                                                              (ppm)    (ppm)    pentyl)-erucamide                                                                      (ppm)                                                                              C.O.F.                                                                            Adhesion                               __________________________________________________________________________    1  2000     0        0        1500 0.18                                                                              0                                      2  0        2000     0        1500 0.16                                                                              1.0                                    3  0        0        2000     1500 0.17                                                                              1.2                                    __________________________________________________________________________

In each experiment, the printability was good.

It can be seen from the foregoing test data that the incorporation ofN-ethanol erucamide and N-ethanol oleamide of the present invention intopolyolefin films, especially into low density polyethylene, improves theadhesion of water-based ink to the polyolefin while providing good slip.Furthermore, the N-ethanol acid amide can be used in combination with afinely divided inorganic material with enhanced results. Thiscombination of components enhances the increase in slip and adhesion ofwater-based inks of the polyolefinic compositions. Included among thefinely divided inorganic material useful in the present invention aresilica, mica, talc, diatomaceous earth and calcium carbonate generallyhaving a particle size of from 0.1 to about 100 microns. The finelydivided inorganic material is generally used in amounts of from about0.05 to about 1.0, preferably from about 0.1 to about 0.5 weight percentof the weight of the polyolefins polymer. Also the data shows that aprolonged corona discharge treatment will further improve the adhesionof the water-based ink to polyolefins containing the additives of thepresent invention. Other like treatments can also be used with themethods and compositions of this invention.

It should be understood that the embodiments of the present inventionwhich have been described are merely illustrative of a few of theapplications of the principles of the present invention. Numerousmodifications may be made by those skilled in the art without departingfrom the spirit and scope of the invention.

We claim:
 1. A method for improving the adhesion of water-based inks topolyolefin polymers which comprises incorporating into the polyolefinpolymers an effective amount of an N-ethanol acid amide selected fromthe group consisting of N-ethanol erucamide and N-ethanol oleamide. 2.The method of claim 1 wherein there is also added to the polyolefinpolymer an effective amount of a finely divided inorganic material. 3.The method of claim 2 wherein the finely divided inorganic material isselected from the group consisting of silica, mica, talc, diatomaceousearth and calcium carbonate.
 4. The method of claim 1 wherein thepolyolefin polymer is a homopolymer or copolymer of ethylene, or ahomopolymer or a copolymer of propylene.
 5. The method of claim 4wherein the polyolefin polymer is a low density polyethylene.
 6. Themethod of claim 4 wherein the polyolefin polymer is polypropylene. 7.The method of claim 1 wherein the N-ethanol acid amide is N-ethanolerucamide.
 8. The method of claim 1 wherein the N-ethanol acid amide isN-ethanol oleamide.
 9. The method of claim 1 wherein the N-ethanol acidamide is between 0.05 and about 0.20 weight percent of the polyolefinpolymer.